Elsevier

Journal of Biomechanics

Volume 47, Issue 10, 18 July 2014, Pages 2460-2466
Journal of Biomechanics

Increased initial cement–bone interlock correlates with reduced total knee arthroplasty micro-motion following in vivo service

https://doi.org/10.1016/j.jbiomech.2014.04.016Get rights and content

Abstract

Aseptic loosening of cemented tibial components in total knee arthroplasty (TKA) has been related to inadequate cement penetration into the trabecular bone bed during implantation. Recent postmortem retrieval work has also shown there is loss of interlock between cement and bone by resorption of trabeculae at the interface. The goal of this study was to determine if TKAs with more initial interlock between cement and bone would maintain more interlock with in vivo service (in the face of resorbing trabeculae) and have less micro-motion at the cement–bone interface. The initial (created at surgery) and current (after in vivo service) cement–bone interlock morphologies of sagittal implant sections from postmortem retrieved tibial tray constructs were measured. The implant sections were then functionally loaded in compression and the micro-motion across the cement–bone interface was quantified. Implant sections with less initial interdigitation between cement and bone and more time in service had less current cement–bone interdigitation (r2=0.86, p=0.0002). Implant sections with greater initial interdigitation also had less micro-motion after in vivo service (r2=0.36, p=0.0062). This work provides direct evidence that greater initial interlock between cement and bone in tibial components of TKA results in more stable constructs with less micro-motion with in vivo service.

Introduction

Over 600,000 total knee arthroplasties (TKAs) are performed in the US each year and the probability of needing a revision during the lifetime of the patient has been estimated to be 15% for males and 17.5% for females (Losina et al., 2012). Loosening of the tibial component is the most common cause of knee arthroplasty failure, but details about how loosening occurs is not fully understood. Aseptic loosening of cemented implants is often seen as a progression of radiolucent lines on x-ray at the interface between the cement and bone (Schneider and Soudry, 1986). At this point, gaps can form between the cement and bone and are often filled with fibrocartilage tissue (Hori and Lewis, 1982). Poor penetration of cement into the bone bed at the time of surgery increases the propensity for radiolucency formation (Ritter et al., 1994).

Pressurization of cement into trabecular bone results in a mechanical interlock between the cement and bone and this provides the initial fixation for the implant. However, with in vivo service, the trabeculae that interlock with the cement layer can resorb. A recent morphological study of postmortem retrieved tibial trays showed that 75% of the cement–bone interlock was lost within 10 years of in vivo service (Miller et al., 2014). These findings suggest that the fixation that exists at the completion of surgery does not remain over the functional lifetime of the joint arthroplasty. Excessive trabecular bone resorption at the cement–bone interface could contribute to increased micro-motion and eventual implant loosening.

The goal of this study was to determine the influence of the initial state of cement–bone interlock on the loss of trabecular interlock and interface micro-motion following in vivo service. This was accomplished using en bloc postmortem-retrieved tibial components from TKAs; these implants were not revisions obtained for a loose implant. We hypothesized that tibial components with more initial interlock between cement and bone would maintain more interlock with in vivo service and have less micro-motion at the cement–bone interface.

Section snippets

Specimen preparation

Ten fresh-frozen cemented total knee arthroplasties (TKAs) were obtained en bloc from the Anatomical Gift Program at SUNY Upstate Medical University (Table 1). All components had metal tibial trays with stems/keels and polyethylene inserts. All tibial components were determined to be radiographically well fixed (radiolucent lines less than 2 mm in 1 or fewer zones).

Articulating surface wear was quantified using the grading scheme of Hood et al. (1983) for abrasion, burnishing, cement debris,

Results

The lateral specimen from Implant C failed during preparation due to a very weak cement–bone interface leaving 23 test specimens from 12 TKAs for testing and analysis. Specimens had a wide range of cement–bone interlock, from laboratory prepared specimens where there was no resorption of the trabecular bone (Fig. 4A), to postmortem retrievals with some remaining interlock (Fig. 4B), to specimens with little or no bone in the interdigitated region (Fig. 4C and D). The mean initial

Discussion

Postmortem retrieved tibial components from cemented total knee arthroplasties (TKA) were used to determine if implants that started with better initial interlock to bone maintained interlock with in vivo service, and also had greater mechanical stability. There was a loss of cement–bone interlock with in vivo service, and specimens with greater initial interlock maintained more interlock with time in service. With functional loads applied to the sagittal sections, there was less interface

Conflict of interest statement

Timothy Izant serves as a paid consultant for Stryker Orthopaedics for clinical total joint replacement studies unrelated to the content of this manuscript. All other authors have no conflicts of interest to disclose.

Acknowledgments

The research reported in this publication was supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health under Award number AR42017. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. The authors would like to acknowledge the assistance of Dan Jaeger for providing the postmortem retrievals and tissue from the SUNY Upstate Anatomical

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